[Bug] The filter calc operator exit when filter push down

### Search before asking

- [X] I searched in the [issues](https://github.com/apache/incubator-paimon/issues) and found nothing similar.

### Paimon version

0.5

### Compute Engine

flink1.14

### Minimal reproduce step

CREATE CATALOG my_catalog
WITH
('type' = 'paimon', 'metastore' = 'hive' ....
) ;

CREATE
TABLE printsink
(
user_id BIGINT,
item_id BIGINT,
behavior STRING,
dt STRING
)
WITH
( 'connector' = 'print'
) ;

INSERT INTO printsink
SELECT
user_id,
item_id,
behavior,
dt
FROM
my_catalog.tmp.paimon_test_table13 where dt = '2023-08-30'

### What doesn't meet your expectations?
The filter calc operator exit when filter push down, is this correct ?


optimize result:
Sink(table=[default_catalog.default_database.printsink], fields=[user_id, item_id, behavior, dt])
+- Calc(select=[user_id, item_id, behavior, _UTF-16LE'2023-08-30':VARCHAR(2147483647) CHARACTER SET "UTF-16LE" AS dt])
+- ChangelogNormalize(key=[dt, user_id])
+- Exchange(distribution=[hash[dt, user_id]])
+- Calc(select=[user_id, item_id, behavior, dt], where=[=(dt, _UTF-16LE'2023-08-30':VARCHAR(2147483647) CHARACTER SET "UTF-16LE")])
+- TableSourceScan(table=[[my_catalog, tmp, paimon_test_table13, filter=[equals(dt, '2023-08-30')]]], fields=[user_id, item_id, behavior, dt])

**When scan push down close:**


2023-09-06 14:05:20.166 DEBUG [Flink-DispatcherRest:t-thread-1] o.a.f.t.planner.plan.optimize.program.FlinkChainedProgram - optimize physical_rewrite cost 100 ms.
optimize result:
Sink(table=[default_catalog.default_database.printsink], fields=[user_id, item_id, behavior, dt])
+- Calc(select=[user_id, item_id, behavior, _UTF-16LE'2023-08-30':VARCHAR(2147483647) CHARACTER SET "UTF-16LE" AS dt])
+- ChangelogNormalize(key=[dt, user_id])
+- Exchange(distribution=[hash[dt, user_id]])
+- Calc(select=[user_id, item_id, behavior, dt], where=[=(dt, _UTF-16LE'2023-08-30':VARCHAR(2147483647) CHARACTER SET "UTF-16LE")])
+- TableSourceScan(table=[[my_catalog, tmp, paimon_test_table13]], fields=[user_id, item_id, behavior, dt], hints=[[[OPTIONS options:{scan.push-down=false}]]])

### Anything else?

_No response_

### Are you willing to submit a PR?

- [ ] I'm willing to submit a PR!

No source files or tests are named. Start by reproducing the minimal Flink 1.14 SQL query and compare the optimizer plans with scan pushdown enabled and disabled; determine whether the remaining Calc filter is expected, then use the relevant planner or scan-pushdown tests to define the corrected behavior.

Written by the indexing model from the issue text.